Figure 4

Evolution of the HRV indices before SBT. The temporal parameters SDNN and RMSSD, and the frequency parameters, \({\text{ P }}_{{\rm VLF}}\), \({\text{ P }}_{{\rm HF}}\) and \({\text{ P }}_{{\rm LF}}^n\) are represented. Green and Red boxplots represent the patients of the S-group and the F-group, respectively. The p-value comparing each half hour is represented in the right axis, from 0 to 1, and the dotted line represents the \(p=0.05\) threshold. Black asterisks indicate statistical significance with \(p \le 0.05\). Blue stars above p-values indicate medium effect size with Cohen’s \(d \in [0.5,0.8)\), and blue crosses indicate small effect size with Cohen’s \(d \in [0.2,0.5)\).